Best method to determine span direction of and RC slab

[patswfc]

I'm currently working on a small refurb job in the UK. The building is traditional load bearing masonry and generally only 1 storey high with a timber flat roof. Part of the building is 2 storeys high. This part has a reinforced concrete slab on the 1st floor(2nd floor for any american readers) with several walls built right up to the underside of the slab.
Looking at the layout of the walls i think that the slab is 1 way spanning, but i would like to know what methods are available to check this assumption. If dont want to remove any walls that i think are non load bearing that turn out to be load bearing walls!!
I'm thinking of asking for a few cores to be taken to expose the rebar and try and determine from this or to use a cover meter to see the direction of the rebar, but if there is distribution rebar running in the other direction to the span, which there should be, then will I get any useful readings from the cover meter? What do you think is the best method or do you know of any other methods.

Thanks

 

[JAE]

You would have to look at the size and spacing of the reinforcing (both top and bottom steel) to get an idea of how the slab was originally designed. Also looking at the aspect ratio of the slab in plan (width vs. length) might give you hints as to how it was designed.

To do this you'd probably have to have a pretty exhaustive investigation of all the reinforcement in the slab - which would be more like the rebar locators you mention.

Just getting a few local cores wouldn't give you enough info in my opinion.

 

[msquared48]

You might also consider cracking patterns in the slab, if there are any.

Sometimes, particularly over a support, it can tell you a lot about the reinforcing pattern and bearing lines.

Mike McCann
MMC Engineering

 

[engstructural]

I would get a number of small holes opened up in the slab to inspect the size and direction of the reinforcement, cover, depth of slab etc.
I would also check the spans in either direction, if possible get a small hole opened up at the existing supports.

Assuming the proportion of the slab means it could be either single span or 2way spanning I would run a design for either case any you would for a new slab only using the info from above and see if the work (use RCC spreadsheets). I would tend to use a low concrete compressive strength unless i know otherwise (20N/mm2).

If it works either way and the support and span reinforcement is OK the it works.

It could have been designed as single span but have enough distribution reinforcement to act as 2way.